With the discovery of living cationic polymerization, the synthesis of polyisobutylenes (PIBs) with controlled molecular weight and quantitative end functionality was made possible. Today, it is known that allyl-terminated polyisobutylenes can be quantitatively endlinked by hydrosilylation with molecules containing an SiH moiety. This reaction results in the formation of a hydrolytically stable Si—C bond. Heretofore, however, research into the usefulness of the quantitative end functionality of polyisobutylene and the ability of allyl-terminated PIBs to be endlinked via hydrosilylation with siloxane compounds has centered on the production of star polymers and star block copolymers. For instance, U.S. Pat. No. 5,663,245 teaches the synthesis and characterization of multi-arm star polymers comprising polyisobutylene arms emanating from a well-defined siloxane core. Star block copolymers have been produced using polyisobutylene-b-polystyrene arms emanating from a well-defined siloxane core. There has been little, if any, study into the usefulness of this synthesis reaction in the production of networks such as two-component networks or multi-block copolymers.
The polymeric networks of the present invention, and particularly two-component networks (BCNs), should be distinguished from more traditional interpenetrating polymer networks (IPNs). A BCN is defined as a single elastomeric network comprising two chemically different covalently bonded sequences; whereas, an IPN consists of two or more unlinked independent networks. The distinction to be made is significant in that the polymers in the IPNs are not linked chemically, but rather are two separate networks tangled within one another. Most two-component systems studied to date concern IPNs, with very few studies having been performed using BCNs.
It will be appreciated that multi-block copolymers are like BCNs in that they also comprise two chemically different covalently bonded sequences, but are not crosslinked in the manner that BCNs are crosslinked. Rather, multi-block copolymers are linear blocks of at least two polymers, such as, for the present invention, polyisobutylene (-A-) and any of a number of bi-functional linear polysiloxanes (-B-), endlinked together to form multiple block copolymers (-A-B-)n. Notably, these block copolymers are synthesized differently from “regular” block copolymers in that the polymers (-A-) and (-B-) are already formed before endlinking takes place. However, they are not “two-component networks” either, as defined hereinabove, because they are not crosslinked and, therefore, are not elastomeric in nature and are soluble in various solvents. BCNs traditionally have required that the two crosslinked components at least contribute theoretically to the physical and chemical characteristics of the polymeric networks. That is, the properties of the two-component network will reflect those of the individual components. For example, two-component networks containing polyisobutylenes and polysiloxanes may be of great interest to the extent that polyisobutylene is known for low cost, superior mechanical properties, extremely low gas permeability and excellent environmental, hydrolytic and high temperature resistance while, in contrast, siloxanes are relatively expensive, have poor mechanical properties, but excel in regard to high gas permeability, low surface energy and bi-compatibility.